Use of the designer drug, 3,4-methylenedioxymethamphetamine (MDMA) has become increasingly popular with young adults largely due to the overwhelming belief that it is a "safe" drug; however research has shown that this assumption is false. Animal and human research have indicated that MDMA targets serotonin (5- HT) neurons. Both the hippocampus and the amygdala, areas rich in 5-HT neurons, have been shown to have reduced 5-HT binding in MDMA users. Recent research has also implicated the dopaminergic system in MDMA neurotoxicity. Studies have also shown that MDMA users exhibit cognitive deficits associated with hippocampal and amygdaloid function (e.g., learning/memory, impulsivity) as well as striatal function (procedural memory and motor functions). It is, therefore, important to take a closer look at hippocampal, amygdaloid and striatal structures to clarify the effect of MDMA on each structure and the relationship between drug-induced damage and neuropsychological function. No study to date has examined the structural consequences in the brain of MDMA use; i.e., whether brain structures are altered as a result of MDMA use. It would be important to determine if any such changes are clinically relevant and if so, whether the extent of MDMA use has a significant influence. Further, most studies have either neglected to include a control group or have only compared data between MDMA users and normals. While these data are valuable, it is important to remember that most MDMA users have used other illicit drugs, particularly marijuana; thus, the question still remains whether deficits are due to MDMA specifically or to other drugs. Lastly, most previous studies have neglected to compare males and females to determine differences in drug effects between the sexes. Since gender differences have been found in brain structural volumes and cognition between normals as well as psychiatric groups (e.g., schizophrenia), it is important to examine whether MDMA has a different effect on males vs. females. This study will help elucidate the impact of MDMA on temporal lobe physiology and subsequent learning/memory, emotional recognition/differentiation and impulsivity/risk-taking between MDMA users, polydrug users (i.e., non-MDMA drug users) and normals. Further, gender differences in response to MDMA use will be investigated.